NAME

       sd_login_monitor_new, sd_login_monitor_unref, sd_login_monitor_flush, sd_login_monitor_get_fd,
       sd_login_monitor_get_events, sd_login_monitor_get_timeout, sd_login_monitor - Monitor login sessions,
       seats, users and virtual machines/containers

SYNOPSIS

       #include <systemd/sd-login.h>

       int sd_login_monitor_new(const char* category, sd_login_monitor** ret);

       sd_login_monitor* sd_login_monitor_unref(sd_login_monitor* m);

       int sd_login_monitor_flush(sd_login_monitor* m);

       int sd_login_monitor_get_fd(sd_login_monitor* m);

       int sd_login_monitor_get_events(sd_login_monitor* m);

       int sd_login_monitor_get_timeout(sd_login_monitor* m, uint64_t* timeout_usec);

DESCRIPTION

       sd_login_monitor_new() may be used to monitor login sessions, users, seats and virtual
       machines/containers. Via a monitor object a file descriptor can be integrated into an application defined
       event loop which is woken up each time a user logs in, logs out or a seat is added or removed, or a
       session, user, seat or virtual machine/container changes state otherwise. The first parameter takes a
       string which can be seat (to get only notifications about seats being added, removed or changed), session
       (to get only notifications about sessions being created or removed or changed), uid (to get only
       notifications when a user changes state in respect to logins) or machine (to get only notifications when
       a virtual machine or container is started or stopped). If notifications shall be generated in all these
       conditions, NULL may be passed. Note that in the future additional categories may be defined. The second
       parameter returns a monitor object and needs to be freed with the sd_login_monitor_unref() call after
       use.

       sd_login_monitor_unref() may be used to destroy a monitor object. Note that this will invalidate any file
       descriptor returned by sd_login_monitor_get_fd().

       sd_login_monitor_flush() may be used to reset the wakeup state of the monitor object. Whenever an event
       causes the monitor to wake up the event loop via the file descriptor this function needs to be called to
       reset the wake-up state. If this call is not invoked the file descriptor will immediately wake up the
       event loop again.

       sd_login_monitor_get_fd() may be used to retrieve the file descriptor of the monitor object that may be
       integrated in an application defined event loop, based around poll(2) or a similar interface. The
       application should include the returned file descriptor as wake-up source for the events mask returned by
       sd_login_monitor_get_events(). It should pass a timeout value as returned by
       sd_login_monitor_get_timeout(). Whenever a wake-up is triggered the file descriptor needs to be reset via
       sd_login_monitor_flush(). An application needs to reread the login state with a function like
       sd_get_seats(3) or similar to determine what changed.

       sd_login_monitor_get_events() will return the poll() mask to wait for. This function will return a
       combination of POLLIN, POLLOUT and similar to fill into the .events field of struct pollfd.

       sd_login_monitor_get_timeout() will return a timeout value for usage in poll(). This returns a value in
       microseconds since the epoch of CLOCK_MONOTONIC for timing out poll() in timeout_usec. See
       clock_gettime(2) for details about CLOCK_MONOTONIC. If there's no timeout to wait for this will fill in
       (uint64_t) -1 instead. Note that poll() takes a relative timeout in milliseconds rather than an absolute
       timeout in microseconds. To convert the absolute 'us' timeout into relative 'ms', use code like the
       following:

           uint64_t t;
           int msec;
           sd_login_monitor_get_timeout(m, &t);
           if (t == (uint64_t) -1)
                   msec = -1;
           else {
                   struct timespec ts;
                   uint64_t n;
                   clock_getttime(CLOCK_MONOTONIC, &ts);
                   n = (uint64_t) ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
                   msec = t > n ? (int) ((t - n + 999) / 1000) : 0;
           }

       The code above does not do any error checking for brevity's sake. The calculated msec integer can be
       passed directly as poll()'s timeout parameter.

RETURN VALUE

       On success sd_login_monitor_new(), sd_login_monitor_flush() and sd_login_monitor_get_timeout() return 0
       or a positive integer. On success sd_login_monitor_get_fd() returns a Unix file descriptor. On success
       sd_login_monitor_get_events() returns a combination of POLLIN, POLLOUT and suchlike. On failure, these
       calls return a negative errno-style error code.

       sd_login_monitor_unref() always returns NULL.

NOTES

       The sd_login_monitor_new(), sd_login_monitor_unref(), sd_login_monitor_flush(),
       sd_login_monitor_get_fd(), sd_login_monitor_get_events() and sd_login_monitor_get_timeout() interfaces
       are available as shared library, which can be compiled and linked to with the libsystemd-loginpkg-
       config(1) file.

SEE ALSO

       systemd(1), sd-login(3), sd_get_seats(3), poll(2), clock_gettime(2)

systemd 204                                                                              SD_LOGIN_MONITOR_NEW(3)